Muscular dystrophies (MD) are a group of more than 30 genetic diseases characterized by progressive weakness and degeneration of the skeletal muscles that control movement. Duchenne muscular dystrophy (DMD) is one of the most severe forms of MD that affects approximately 1 in 5000 boys and is characterized by progressive muscle weakness and premature death. Cardiomyopathy and heart failure are common, incurable and lethal features of DMD. The disease is caused by mutations in the gene encoding dystrophin (DMD), a large intracellular protein that links the dystroglycan complex at the cell surface with the underlying cytoskeleton, thereby maintaining integrity of the muscle cell membrane during contraction. Mutations in the dystrophin gene result in loss of expression of dystrophin causing muscle membrane fragility and progressive muscle wasting.
Despite intense efforts to find cures through a variety of approaches, including myoblast transfer, viral delivery, and oligonucleotide-mediated exon skipping, there remains no cure for any type of muscular dystrophy. The present inventors recently used clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9)-mediated genome editing to correct the dystrophin gene (DMD) mutation in postnatal mdx mice, a model for DMD. In vivo AAV-mediated delivery of gene-editing components successfully removed the mutant genomic sequence by exon skipping in the cardiac and skeletal muscle cells of mdv mice. Using different modes of AAV9 delivery, the inventors restored dystrophin protein expression in cardiac and skeletal muscle of mdx mice. The mdx mouse model and the correction exon 23 using AAV delivery of myoediting machinery has been useful to show proof-of concept of exon skipping approach using several cuts in genomic region encompassing the mutation in vivo. Recent work with ΔEx50 mouse model demonstrated an optimized the method for dystrophin reading frame correction using a single guide RNA that created reframing mutations and allowed permanent skipping of exon 51. However, there is a lack of other models for the various known DMD mutations, and for new mutations that continue to be discovered.